Bromo butadiene polymers and method of producing same



Patented Mar. 13, 1934 PATENT OFFICE BROMO BUTADIENE POLYMERS AND METHODOF PRODUCING SAlVIE Wallace H. Cal-others and Arnold M. Collins,Wilmington, Del., assignors to E. I. du Pont de Nemours & Company,Wilmington, Del, a corporation of Delaware No Drawing. Application May14, 1931, Serial No. 537,492

' 20 Claims.

This invention relates to a new class of organic compounds and to themethod of their preparation. More particularly it relates to polymersobtained from bromo-2-butadiene-1,3.

Prior art Fifty-two grams of monovinylacetylene is placed in a pressurebottle together with 185 cc.-

of concentrated hydrobromic acid (approximately 11 normal) and 35 g. ofcuprous bromide, and the bottle is closed and shaken vigorously for sixhours or longer. The aqueous solution is then separated from the oilylayer and the latter is washed with water, stabilized with catechol, anddistilled preferably under diminished pressure in a current of nitrogenor carbon dioxide. The fractions collected are: bromo-2butadiene-l,3boiling at 38-40" C. at 155-165 mm. (about 32 g.), and dibromobuteneboiling at 88-92" C. at 56-459 mm. (about 48' g.) Each of thesefractions may be purified further by redistillation.

Agents suitable for stabilizing the addition products ofmonovinylacetylene and hydrobromic acid may be present during thereaction or added subsequently. Such agents are exemplified byinhibitors, such as catechol as in the above Example A, hydroquinone,pyrogallol, trinitrobenzene, iodine, diphenyl guanidine,m-toluylenediamine, as described fully in the Carothers and Collinsapplication referred to above;

Object of invention In accordance with the teachings of the presentinvention, it has been found that bromo-Z- butadiene-L3 may be readilypolymerized under a wide variety of conditions with the production ofnovel and useful products. I

An object of this invention, therefore, pertains to the polymerizationof bromo-2-butadiene-l,3. A further object relates .tothe preparation ofnew anduseful materials, and particularly to the preparation of strong,tough, elastic masses, re-

(ill. 260-6) sistant to the action of solvents and chemical agentsgenerally, and resembling vulcanized natural rubber.

lhe mode of effecting the polymerization of bromo-2-butadiene-L,3 iscapable of a considerable variation due to the number of conditionswhich may influence the polymerization, and the resulting polymerslikewise'have widely varying characteristics. One method of effectingthe polymerization-is illustrated as follows:

Example I A sample of bromo-2-butadiene-l,3, freed by distillation ofany impurities which might have m inhibiting eiiect on the course oi thereaction is placed in a closed vessel containing a small m amount oi air(about 5% by volume) and the vessel is allowed to stand at 25 C. andatmospheric pressure in the absence of direct light. Under theseconditions, the bromo-butadiene, which is at first a moderately heavy,mobile, 3Y pale yellow liquid gradually changes in consistency. After 12tol5 hours, it has become much more viscous; later it sets to a stickyjelly, and finally, after about 10 days, it is converted to a dark,opaque, strong, tough mass, having a cer- 39 tain amount of elasticityand bearing a resemblance to vulcanized natural rubber. A typicalspecimen of this product was shown to have a specific gravity of Ll l.

As indicated in Example I, there is a continu- 35 ous change in theproperties of the material undergoing polymerization until thepolymerization has become complete. The special properties of theintermediate, incompletely polymerized mixtures sometimes make advisabletheir use as 90 'such, either in the state of viscous liquids, or in thestate of sticky or plastic polymers, with or without the removal of theunpolymerized bromobutadiene.

For example, soluble and plastic products are readily obtained byinterrupting the polymer'ization when the product is in the form of aviscous liquid or a soft jelly and separating the unchangedbromo-butadiene from its polymer. This separation may be efiected byallowing the unchanged bromo-butadiene to evaporate or distill, or byprecipitating the polymer with the aid of some solvent such as alcoholor acetone which is capable of dissolving the bromo-butadiene but notits polymer, or the separation may be eifected by other suitable means.The polymer thus obtained can be mixed with pigments, dyes, fillers,stabilizersfvulcanizing agents, etc., and either with or without suchadditions it can be molded. A particularly desirable modifying 'agent iszinc oxide. The polymerization can then be caused to proceed tocompletion by the action of heat to yield a finished article in the formof a tough, elastic, insoluble, non-plastic mass. The plastic, solublepolymers isolated by 'the methods indicated above from incompletelypolymerized bromo-butadiene may also be dissolved in suitable solventssuch as toluene,

chloroform, trichloroethylene, etc. to produce solutions suitable foruse as coating and impregnating agents, and as cements.

The polymerization of bromo-Z-butadiene-LS is greatly affected by thepresence of oxygen, the rate of polymerization increasing upon exposureto an increased amount and concentration. of oxygen. Thus the rate ofpolymerization is greater under an atmosphere of oxygen than der anatmosphere or" air, other conditions being the same. The rate of surfaceto volume when the bromo-butadiene is exposed to oxygen has a directbearing on the rate of polymerization, a greater proportionate amount ofexposed surface causing an increase in the rate of polymerization.

Certain oxidizing catalysts markedly increase the rate ofpolymerization, and the rate will, in general, be proportional to thequantity or cat alyst present, the quantity of any particular catalystnecessary to produce a given rate of polymerization being easilydetermined by enperiment. The following peroxides have been found to beadaptable for increasing the rate or polymerization: benzoyl peroxide,oxidized turpentine, and inorganic peroxides such as those sodium, lead,and hydrogen.

The effect of light on the polymerization. rate is similar to that ofoxygen. Hence exposure to direct light, particularly ultraviolet and theshorter light waves of the visible spectrum, greatly increases the rateof polymerization, t intensity of the light, and the ratio of expo-sec.surface to volume directly affecting the poly meriaation.

Elevated temperature and. increased pres"- sure likewise acceleratepolymerization or Torontobutadiene, with an accompanying effect on thecharacter of the product. All -l the conditions which affect the rate ofpolymerization, a" the same time afiect many of the characte stics theproduct, e. g, its color, density, l -ciness, strength, elasticity,plasticity, etc, and the con ditions under which polymerization is totake place must be controlled according to the product desired, as wellas with respect to the optimum. rate of polymerization.

The rate of polymerization may he reduced by working at low temperaturesor by the addition of solvents or diluents, or of inhibitors oi? polymerization, examples of which are given below. As in the case ofconditions which accelerate polymerization, these methods whichpolymerlzation also influence the course of the reactlon andthe natureof the products obtained. Thus solvents, diluents, and inhibitors areparticularly useful in controlling the reaction so as to prevent orreduce the formation of the insoluble, completely polymerized productsand increase the yield of the plastic, soluble polymers.

As solvents or diluenm, we may use a wide variety of organic compounds,including, as shown below, hydrocarbons, halogenated hydrocarbons,alcohols, ethers, and esters. These sol vents and diluents may beconveniently classified as follows:

ranging from 014.0%.

(1) Volatile solvents for both bromo-2-butadime-1,3 and its polymers,such as benzene, xylene, carbon disulfide and carbon tetrachloride.These give rise to more or less viscous solutions ofbromo-2-butadiene-l,3 polymers which may be used directly as coatingcompositions, cements, and impregnating agents, with or withoutincorporation of pigments, dyes, fillers, and other modifying agents. Onremoval of the volatile solvent, 9. plastic polymer ofbromo-Z-butadiene- 1,3 remains. If desired, this may be furtherpolymerized to an insoluble form by the action of heat.

(2) Non-volatile or high-boiling solvents or diluents such as refinedmineral oil, diphenyl ether, linseed oil, and tricresyl phosphate. Thesesubstances remain with the brdmo-2-butadiene- 1,3 after itspolymerization, forming, in general, plastic,'homogeneous, solublemasses. The nonvolatile solvent or diluent often functions a softenerfor the polymer yielding products which are more plastic and morepliable than the pure polymers.

(3) Solvents for bromo-2-butadiene-1,3 which are themselves capable ofpolymerization, for example isoprene and styrene. These substances "mayreact under the conditions used for the polymerization of thebromo-.-2-butadiene-l,3 either by normal polymerization or by so-calledcross polymerization with the bromo-Z-butacliche-1,3 in which moleculesof the latter combine with molecules of the polymerizablc solvent withthe formation of complex. substances of high molecular weight.

(4) Solvents for bromo-2butadiene-i,:l which are non solvents for itspolymers, example ethyl alcohol. When such. solutions of the monomer arepolymerized, the polymer separates as soon as formed and is particularlylight in color and free from odor.

The ffiolymerization oi these solutio s may be brought about by any ofthe metho already desc ibed for the polymerization i OHIO--2-hutaoienedfi. The concentration o the solutlons may be varied over widelimits. A 543% solution is suitable for most purposes,

t me be used as, for example, quinones, amines, aromatic nitrc composulfur compounds, such as mere ethers, and free halogens. Polyliyclricphenols, such as 'hydroquinone and pyrogallol are e the most active ofthese inhibitors. Satmotion of bromo-2-butadiene-i,3 with one of this atroom temperature, substantially prevents its polymerization for longperiods of time under ordinary conditions and in the absence of largeamounts of oxygen. Hence they are useful preservingbrozno-2-butadiene-L3 in the unpoiyrnerized state or for arresting itspolynierizm tion when only partly complete. Other inhibitors, such asiodine and trlnitrobenzene, retard the polymerization without entirelypreventing it. They are useful in controlling the polymerization, andespecially in retarding the formation of the insoluble polymers andhence increasing the yield of the soluble, plastic type. For thispurpose,.they are ordinarily used in amounts Very small amounts of themore active inhibitors also have the same eflect. Since the modificationof' the properties of the polymers rather than a decrease in the rate ofpolymerization is in many cases the primary object in the use ofinhibitors, it is oiten desirable to accelerate the polymerization inthe presence of inhibitors by the application of heat. pressure, light,etc. Furthermore, it is often advantageous polymerize in the presence ofboth solvents and inhibitors.

The plastic polymers prepared in the presence of solvents and/orinhibitors resemble the pies tic products obtained above by arrestingthe I polymerization of bromo-2-butadiene-1,3 before formation ofsubstantial amounts of the insoluble elastic polymer. They can,therefore, be used in much the same way' as natural unvulcanized rubber.For example, fillers, pigments, dyes, and other compounding ingredientsknown to the rubber art may be incorporated by milling or otherwise, andthe resulting masses molded into any desired shape, and finally furtherpolymerized to form products resembling compounded vulcanized naturalrubber. Or, alternatively, the plastic polymers may be dissolved inrubber solvents such as'benzene and used as coating compositions,cements, or impregnating agents, with or without the incorporation ofpigments, dyes, fillers, and other modifying agents.

It has been found that the polymerization. of bromo-2-butadiene-1,3 canbe effected with particular facility when it is suspended in water inthe form of an aqueous emulsion. Such emulsions are readily prepared bystirring together or homogenizing water and bromo-2-butadiene-i,3 in

.the desired proportions in the presence oil a suit= able emulsifyingagent, for example, sodium oleate.. v

The following example illustrates the polymerization ofbrorrio-Z-butadiene-Lt in aqueous emulsion:

' Example H One volume of bromo-2-butadiene-i,3 is emulsified bystirring it with one volume of a 2% aqueous suspension of sodium oleatecontaining 1% of its weight of catechol. After three days standing atordinary temperature, the emulsion is completely polymerized yielding awhite, millr lilre liquid containing the polymer in suspension andresembling natural latex. When the emulsion is spread out in a thinlayer on a plate of porous porcelain, the water evaporates and therere-' mains an opaque, cream-colored, strong, tough, flexible, somewhatelastic film or'sheet. it has a very smooth, soft surface, and undergoesno change in properties on being freely exposed to the air for onemonth. The polymerization of such an emulsion in the absence of thecatechei is much more rapid and the product is In any case the syntheticlatex may be protect ed against spontaneous coagulation by making itslightly alkalinegfor example. by addition of ammonium hydroxide orsodium carbonate.

The emulsion of bromo-2-butadiene-l,3 may bepolymerized readily even inthe absence oi.

the factors which accelerate the polymerization of bromo-2-butadiene-L3,but light, elevated temperature and pressure, oxygen and oxidizing cat,alysts may be used where it is desired to increase the rate ofpolymerization or to vary the character of the product accordingly.

Retarding influences, such as inhibitors, as exemplified by catecholin'ExainpleH, may also be used to-assist in controlling the polymerize.

, tion and in modifying the properties of the final 'erably, largerproportions of "the product. The ratio of bromo-2-butadiene-L3"to waterused in Example 11 may be varied considbromo-z-butato impregnate and/ orcoat porous or bibulous ma- 1 action of solvents or chemical agents aredesired.

dime-1,3 giving viscous dispersions or non-fluid pastes. Otherdispersing agents may be used in place in sodium oleate, for examplesulfonated castor oil, triethanolamine oleate, and magnesium linoleate.The properties of the latex and of the products derived from it may befurther varied by the addition of such modifying agents as proteins, forexample albumin, and gums such as gum arabic.

The latex may be made to yield strong, elastic films as described aboveor may be coagulated, for example by the addition of dilute acetic acidto yield the solid polymer. The latex may also be used for otherpurposes for which natural latex is used, such as the impregnation ofcloth, paper and other porous materials.

The polymers of bromo-2-butadiene-i,3 described above, irrespective ofthe method by which they are formed, are preferably stabilized againstdeterioration by aging by one or more of the 95 methods to be described.Substances capable of prolonging the life of the polymers includeordinary rubber antioxidants, such as the aromatic amines, phenols, andthe natural rubber antioxidants which may be extracted from variousnatural rubbers, for example by means of acetone. These function byinhibiting the oxidation of the polymersof bromo-2-butadine-1,3. Inaddition to these, a class of compounds known as acid ac ceptors, thatis, basic substances or other substances capable of combining withacids, also act as preservatives for the synthetic rubber by com biningwith traces of acid which are formed in the polymers under certainconditions and which in the free state would cause deterioration. it upwill be seen that many of these preservatives also belong to otherclasses of substances used in the preparation of the polymers and may,therefore, serve a double purpose. Thus manyof the anti oxidants arealso inhibitors of polymerization 115 while many acid acceptors alsofunction as sta bilizers of the emulsions against spontaneouscoagulation ,(sodium carbonate) or as pigments (ZLYIO oxide) or asemulsifying agents (sodium oleate). These preserving agents may, in manycases, be added previous to the polymerization, or may be incorporatedinto the plastic polymers by milling, or may be dissolved or dispersedin. the solutions of polymers, or may be applied to solid polymers inthe form of a solution which isabsorbed by the polymer, or may bedissolved or dispersed in the aqueous emulsions or dispersions ofbromo-2= butadiene-lfi or its polymers.

It will be seen from the above description, that bromo-2-butadiene-l,3may readily be po1yrner 13 ized under a wide variety of conditions toyield useful products. The polymers obtained or their solutions oremulsions may be used to prepare shaped articles, films and protectivecoatings and terials such as cloth or paper; and they are particularlyvaluable in connection with such uses when the peculiar advantages ofhigh density, great toughness, or exceptional resistance to the Theabove description is to be construed as illus== Y trative only and notas limiting the scope of the invention. The different features of the imventioh are capable of wide variations, and such changes as are withinthe spirit of the invention are comprehended by the scope of the claims.

We claim:

, 1. A polymer of bromo-z-butadiene-m.

2. A plasticpolymer of bromo-2-butadiene-1,3,

soluble in the usual rubber solvents. I

3. An elastic, non-plastic polymer of bromo- 2-butadiene-1,3.

4. A process which comprises polymerizing bromo-2-butadiene-1,3.

5. A process which comprises polymerizing bromo-2-butadiene-1,3 in thepresence of an agent which increases the rate of polymerization.

6. A process which comprises polymerizing bromo-2-butadiene-1,3 in thepresence or an agent which decreases the rate of polymerization.

7. A process which comprises polymerizing bromo-2-butadiene-1,3, in thepresence of a solvent for the bromo-2-butadiene-1,3.

8. A process whch comprises polymerizing bromo-2-butadiene-1,3 in thepresence of a material which is a. solvent" for the bromo-2-butadienel,3and for the polymers of bromo-2-butadime-1,3. I

9. A process which comprises polymerizing bromo-2-butadiene-1,3, andinterrupting the polymerization before the product of polymerization hasreached the insoluble, elastic stage.

10. A process which comprises polymerizing bromo-2-butadiene-1,3, andinterrupting the polymerization before the product of polymerization hasreached the insoluble, elastic stage, then separating the polymer fromany unpolymerized polymerization before the product of polymerizationhas reached the insoluble; elastic stage, then separating the polymerfrom any unpolymerized bromo-2-butadiene-1,3 and further polymerizingthe plastic polymer to the nonpla'stic state.

12. A coating composition comprising a polymer of bromo-2-butadiene-l,3in a fluid state.

bromo-2-butadiene-L3. I 16. A composition comprising essentially apolymer of bromo-2-butadiene-1,3 and a solvent for said polymer.

17. A composition comprising essentially a polymer ofbromo-2butadiene-l,3 and a pigment.

